This invention relates generally to rotation sensing and particularly to ring laser gyroscope rotation sensors having three mutually perpendicular sensing axes. It is also a feature of this invention to offer electrode arrangements for triaxial ring laser gyroscopes having a plurality of anodes and a common cathode for applying electrical energy to the gain medium. It is likewise a feature of this invention to offer specific embodiments of cathodes internal of a ring laser block.
A ring laser gyroscope employs the Sagnac effect to detect rotation. Counter propagating laser beams in a closed path have light frequencies whose difference is directly proportional to the rotation rate of the path about a predetermined axis enclosed by the path. Such axis, when the beam-path is planar, is perpendicular to the plane of the beam-path. The ring laser gyroscope has two counterpropagating beams traversing a closed path. As the path is rotated about a sensing axis, the wave length of one of the beams increases while that of the other decreases. The difference in frequency or beat frequency is a measure of the angular velocity of the gyroscope about that sensing axis. The output beams from the two directions interfere to produce fringes which are measures of the beat frequency. The high optical frequencies of the beams (10.sup.15 Hz) preclude the direct measure to the required accuracy of the optical frequencies.
Three ring laser gyroscopes may be packaged with their sensing axes mutually orthogonal in one thermally stable block. For each sensing axis there is a gas-filled conduit or ring usually disposed in a plane at right angles to the sensing axis for that ring. Each conduit comprises three or more linear legs that preferably (but not necessarily) are of equal length. Each conduit is filled with a gain medium that is typically pumped by a gas ion flow between appropriately positioned electrodes. Each gain medium produces two beams traveling in opposite directions in a closed path in the conduit. Mirrors located at the conduit corners direct the beams around the conduit. Frequencies in the beams for which the optical path length around the conduit equals an integral number of wavelengths are amplified, forming standing waves.
To alleviate the problems of using three separate ring laser gyroscopes to sense rotations about three mutually orthogonal axes, several attempts have been made to construct a ring laser gyro system containing three ring laser gyroscopes in a single block.
U.S. Pat. No. 4,407,583 to Simms discloses a triaxial ring laser gyroscope. Three four-cornered conduits arranged in mutually orthogonal planes at right angles to their respective sensitive axes. Each conduit shares a corner with each of the other conduits such that the conduits are interconnected. This structure uses six mirrors to define the three four cornered conduits.
The three conduits can be machined from a block of material. A cube is a very convenient shape for this purpose. The conduits can be located accurately in mutually orthogonal planes. To energize the gas in the three ring laser conduits, six anodes and a common external cathode are used.
The U.S. Pat. No. 4,477,188 to Stiles is a three axes ring laser gyroscope which uses either one or two external cathodes.
U.S. Pat. No. 3,503,688 to Lechevalier teaches a Multiple Axis Laser Angular Rate Sensor wherein the single cathode extends centrally clear through the laser block.
U.S. Pat. No. 4,616,929 to Bernelin teaches a Triaxial Laser Rate Gyro with a single external cathode.